[The following contains MAJOR spoilers for The Flash Season 4 finale, "We Are the Flash." If you haven't watched it yet, what are you doing here?!]

Ding dong! An unexpected guest dropped by the Allen home in the final moments of tonight's The Flash episode. And just when we thought the crazy had been contained by the demise of The Thinker (Neil Sandilands), things went off the charts once again.

The vaguely familiar face — until now only known as Mystery Girl (played by Jessica Parker Kennedy), who popped up at Iris and Barry's crossover delayed wedding — arrived bearing wishes for Joe and Cecile's newborn. She also brought a revelation a lot of folks had suspected: She's actually Barry and Iris' daughter... from the future! And apparently, she's followed in her daddy's speedy footsteps, big mistakes and all.

The LGBT actress slammed fans for questioning her ability to take on the role.

Below, showrunner Todd Helbing explains to TV Insider what's up.

The secret daughter!

Todd Helbing: The secret daughter, yes! [Laughs]

When did you guys start to think about laying that story out?

It's funny, a year ago, when we pitched Season 4 to the studio and we were talking about Barry and Iris getting married, the question of 'When are they going to have kids?' came up. We were like, 'Well, we have this idea to do this,' and they were like, 'Yes, let's do it!' That was a year ago. Hat's off to Jessica [Parker Kennedy], because when we sat down with her, it was like, 'Look, are you open to basically coming for five scenes in a year, then coming back next season?' It's a big ask for an actor and she's so amazing and cool and great to work with and she was totally down with it.

Nice. The idea of a unified team was delivered nicely in the finale, but you had us a little scared earlier in the season with the possibility of Cisco (Carlos Valdes) opting to leave.

And with any show, there's always the possibility of a cast change that would alter the formulation of the team. Do you ever worry about the team getting too big?

That's certainly a concern. If you look at [past seasons] for instance, Season 1, everybody had their jobs. Their roles were pretty defined, and then as they got caught up in this craziness of meta-humans and Big Bads, things changed. Like Joe (Jesse L. Martin) was in the Cortex and everybody was in there working together and their jobs got less defined.

So, in Season 4, towards the second half of the season, we wanted to redefine where everybody is in this universe, as far as the team and what their roles are. I think next season, we want to do the same thing, even a little bit more so because the cast is expanding a little bit. We're sort of forced to but it helps us story-wise with splitting them off into pairs or pairings. We're going to get Iris (Candice Patton) out in the field again investigating and writing more. And Ralph (Hartley Sawyer), we explored a little bit of his detective side but not really, so next season we're going to dive into that a little bit more. Cisco is going to have a story. It's going to help us, hopefully, and not hurt us.

It might be a stretch to expect Elongated Man to bounce back from DeVoe's attack.

How will Nora's sudden arrival impact Barry and Iris?

A lot of next season is going to be exploring this question of, what is it like to meet your daughter at basically the same age you are? And pretty quick into the season, you're going to learn exactly what time period she's from and what her dynamic is with her parents.

She can actually come back and tell them, 'This is what you've grown into.'

[Laughs] Yeah. It's funny because Barry's learned his lessons from time travel, right? He's made as big a mistake as you could and Nora has made a pretty big mistake and now it's interesting for Barry to be on the other side. He also has to decide what information he wants to get from her and what he doesn't, because he knows the ramifications of knowing that stuff too soon.

That whole space-time continuum thing can really mess things up!

Yes, exactly.

Parents of the year? maybe, but what year?! Candice Patton as Iris West and Grant Gustin as Barry Allen (Katie Yu/The CW)

Have you thought of what villain you'd like for next season?

I think we certainly needed to take a break from Speedsters. I really like the more human qualities of villains than the meta-human qualities, so for next season, we're going to follow that trend.

Do you plan on pulling from The Flash comics or from the wider DC Comics universe?

The Flash comics, but there's always going to be a Speedster component. It's The Flash, so there will be Speedsters, but our main villain next season is a non-Speedster.